internal/graphicsdriver/directx: refactoring: add syscallN
internal/graphicsdriver/directx: refactoring: add syscallN

syscall.SyscallN is available as of Go 1.18 so this change implemented
our original syscallN function.

syscallN also panics when a given function pointer is 0. This helps
debugging especially on Xbox.

Updates #2084

hajimehoshi/ebiten,hajimehoshi/ebiten